Stabilization of cellulosic material by treatment with ferricyanide ion

ABSTRACT

A method of stabilizing a cellulosic material against degradation by an aqueous alkaline medium. The cellulosic material is treated with a ferricyanide ion under alkaline conditions. The preferred application of the method is in the production of pulp for paper making and the preferred cellulosic material is thus wood. The treating with the ferricyanide ion may take place prior to the pulping or during the pulping.

United States Patent 1 1 3,929,559

Procter Dec. 30, 1975 STABILIZATION OF CELLULOSIC 3,663,358 5/1972Falkenhag et al. 162/70 MATERIAL BY TREATMENT WITH 3,883,391 5/1975Phillips 162/70 X FERRICYANIDE ION [75] Inventor: Alan R. Procter, NorthVancouver,

Canada {73] Assignee: MacMillan Bloedel Limited,

Vancouver, Canada [22] Filed: Dec. 16, 1974 [2l] Appl. No.: 533,027

[52] US. Cl 162/70; 8/116 R; 162/90 [51] Int. Cl. D21C 1/00; D21C H06[58] Field of Search 162/70, 90; 8/116 R [56] References Cited UNITEDSTATES PATENTS 3,532,596 10/1970 Bills et a1. 162/70 Primary ExaminerS.Leon Bashore Assistant Examiner-Arthur L. Corbin Attorney, Agent, orFirmLarson, Taylor and Hinds [57] ABSTRACT A method of stabilizing acellulosic material against degradation by an aqueous alkaline medium.The cellulosic material is treated with a ferricyanide ion underalkaline conditions. The preferred application of the method is in theproduction of pulp for paper making and the preferred cellulosicmaterial is thus wood. The treating with the ferricyanide ion may takeplace prior to the pulping or during the pulping.

13 Claims, 1 Drawing Figure UM atent Dec. 30, 1975 3,929,559

RELATION BETWEEN PULP YIELD AND KAPPA NUMBER FOR SODA COOKS OF WESTERNHEMLOCK CHIPS KAPPA NUMBER =SODA PULP USING FERRICYANIDE STABILIZATIONSTABILIZATION OF CELLULOSIC MATERIAL BY TREATMENT WITH FERRICYANIDE IONBACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This inventionrelates to a stabilization of carbohydrate material against degradationby an aqueous alkaline medium.

2. DESCRIPTION OF THE PRIOR ART Paper may be defined as a tissue offibrous cellulosic materials. The individual cellulose fibres of theoriginal raw material from which the paper is made are first separatedfrom one another by chemical or mechanical means and then feltedtogether to form the tissue. The principal source of cellulosic materialused in paper making is wood. It is desirable that the cellulose used inpaper making should be as pure as possible but in wood the cellulosefibres are intimately associated with incrustants, principally lignin.To isolate the cellulose from the incrustants the wood is pulped as thefirst step in the main paper making process.

The pulping of wood to make wood pulp may be divided into four maingroups:

i. Mechanical or ground wood pulp is prepared by a mechanicaldisintegration of the wood in the presence of water. Yields may beapproximately 95%.

ii. Chemi-mechanical pulp is obtained by softening the wood by a verymild chemical treatment without significant delignification and thendisintegratmg the wood by mechanical action. Typically sodium hydroxide,for example at 30 to 80C, is

used. Yields are typically in the range of 80 to 95%. m. Semi-chemicalpulp is obtained by stronger chemreal action than in chemi-mechanicalpulping. Conditrons are such that some delignification occurs. Thechemical action is followed by defibering by mechanical treatment.Typical yields are 55 to 80%. The reagent originally used insemi-chemical pulping was neutral sodium sulfite, that is sodium sulfitebuffered by sodium carbonate. But later it was realized that thereagents useful in the full chemical pulping of wood were useful ifmilder reaction conditions were employed and if it were ensured that thedigestion or pulpmg process was stopped before any major delignificatronoccurred. Thus acid sulfite (calcium bisulfite and sulfuric acid);bisulfite (a mixture of sodium bisulfite and magnesium bisulfite) andsulfate (sodium hydroxide and sodium sulfide) are now used insemi-chemical pulping.

1V. Chemical pulp is obtained by chemical treatment sufficient to removethe interfibre lignin of the wood thus allowing the cellulose fibres toseparate with only minor or no mechanical treatment. A typical yield is42 to 58% depending on the wood used and the digestion chemical.

Chemical pulping has been subdivided to alkaline pulping and acidpulping. Alkaline pulping may be further subdivided into the sodaprocess in which sodium hydroxide is used to carry out the pulpingprocess and the kraft or sulfate process in which sodium hydroxide andsodium sulfide are used.

The present invention finds applications in the alka- Lilrcigdpulpmg ofcarbohydrate material, particularly The original alkaline pulpingprocess was the use of sodium hydroxide. Because of the cost of sodiumhydroxide it was necessary to recover the sodium hydroxide in theresidual or black'liquor and to re-use it. This recovery was byseparation and evaporation of the black liquor, burning and dissolvingthe resultant sodium carbonate in water. Calcium hydroxide was thenadded to the solution to obtain sodium hydroxide. It was later foundthat sodium sulfide in the cooking liquor gave improved dissolution andless degraded pulp. By using sodium sulfate to make up the sodiumhydroxide loss and adding it to the black liquor before burning themakeup sulfate was reduced to the desired sodium sulfide. The use ofsodium sulfate rather than sodium hydroxide for makeup gives the namethe sulfate process. However, the process is principally known as thekraft process.

All the chemical pulping processes suffer from the disadvantage thatcellulose can undergo many chemical transformations. Thus the pulpingprocess, in delignifying wood, also destroys cellulose and theassociated hemicelluloses. Although the kraft process is the most widelyusedalkaline pulping process because of its well-established technologyand ability to produce strong pulps from practically any fibrouslignocellulosic material it has the disadvantages, first, of low yieldand,

' secondly, that it produces an unpleasant odour associated withsulfur-containing gaseous emission. For the past several years it hasbeen a major concern of the pulping industry to find a sulfur-freepulping process in which these emissions would be avoided. One processsuggested for the avoiding of the emissions is the soda processmentioned above. However this process suffers from the disadvantage thateven lower pulp yield is achieved than with the kraft process, again asa result of carbohydrate alkaline degradation.

U.S. Pat. No. 3,532,596 to Bills et al discloses a process for pulpinglignocellulosic material which involves treatment with an aqueoussolution containing cyanide ions. By this means the aldehyde groups inthe carbohydrates are converted to cyanohydrin groups and these groupsthen hydrolyzed into carboxyl groups. Thus the process essentiallyinvolves the incorporation of additional carbon atoms into the chain.The pulping described in U.S. Pat. No. 3,532,596 is an alkaline pulp-U.S. Pat. No. 3,663,358 to Falkenhag et al also discloses the use of thecyanide ion to increase the pulp yield from lignocellulosic material. Inthis patent the pulping is carried out with a bisulfite pulping solutionhaving a pH below 7.

The processes of the above patents proceed by a mechanism similar to theKiliani-Fischer reaction. The mechanism is:

An obvious disadvantage of the processes described in the above patentsis the extreme toxicity of the cyanide ion.

SUMMARY or THE INVENTION The present invention seeks to avoid the abovedisadvantages by providing a method for stabilizing a carbohydratematerial against degradation by an aqueous alkaline medium thatcomprises treating the carbohydrate material with ferricyanide ion underalkaline conditions. The treatment with the ferricyanide ion may becarried out prior to an alkaline pulping process or during that process.The method has the virtue that the stabilized carbohydrate material ismore resistant towards degradation by alkali. It is possible to pulp thestabilized carbohydrate material simply by an alkali, without sulfurcompounds. Thus the method of the invention permits a sulfur-freepulping method that gives higher yields than presently possible withoutthe disadvantage of foul smelling emissions.

In contrast to the mechanism of the above Bills et al and Falkenhagpatents the mechanism of the present process is:

RCHO 2Fe(CN) 2611- RCOOH 2Fe(CN) H2O That is the alkaline ferricyanideacts as an oxidizing agent and is reduced to ferrocyanide. Ferricyanideis a stable ion and does not dissociate significantly into cyanide ions,a considerable advantage from the point of view of toxicity.Furthermore, the ferrocyanide ion is relatively easy to convert back tothe ferricyanide ion, for example, by oxidation with air, oxygen orchlorine. This can be economically attractive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the preferred embodimentsthe carbohydrate material is a lignocellulosic material, for examplewood. The treatment ,with the ferricyanide ion is generally carried outat a pH of about 10. The ferricyanide ion may be added as sodiumferricyanide or potassium ferricyanide. Although the invention has thevirtue that it permits the use of the soda process and obtains goodyields withoutfoul emissions it is also possible to improve the yield ofthe kraft process because of the improved stability of the carbohydratematerial.

The invention is illustrated in the following examples and in theattached drawing, referred to in Example 3.

EXAMPLE 1 Results:

Molarity of Ferricyanide in Pretreatment Hydrocellulose Remaining AfterAlkaline Degradation 0 29 0.01 M 51 0.02 M 66 0.05 M 66 0.2 M 72 Theseresults demonstrate the effectiveness of the method, when used as apretreatment, for stabilizing cellulose towards alkaline degradation.

EXAMPLE 2 In the second series of experiments, potassium ferricyanidewas added to alkaline digestions of hydroce'llulose (100C., 2 hours).

Results:

Molarity of Ferricyanide Hydrocellulose Remaining Added After AlkalineDegradation The results demonstrate the effectiveness of ferricyanide asan addition reagent to an alkaline digestion, for stabilizing cellulosetoward alkaline degradation.

EXAMPLE 3 Ferricyanide Yield Increase Addition Pulp Yield Kappa N0. OverAn Equivalent Soda Pulp At The Same Kappa No.

The Kappa No. is the number of milliliters of O.IN potassiumpermanganate consumed by one gram of dry cellulose pulp under specifiedconditions. It is useful as an index related to the degree ofdelignification attained during the cook.

These results demonstrate the effectiveness of a ferricyanide treatmentfor increasing pulp yield, when compared with the yield vs. Kappa No.relationship for regular soda pulps of the same raw material. Theresults are illustrated graphically in FIG. 1 which compares pulp yieldand Kappa No. for soda cooks of western hemlock chips with and withoutthe ferricyanide.

The stabilizing method appears particularly effective as a pretreatmentfor producing high yield, high Kappa number pulps. These pulps would beparticularly suitable for subsequent delignification with oxygen underpressure to produce high yield bleachable grade chemical pulps, bymethods well known in the art of pulping.

In should be emphasized that the invention is useful in any process forisolating cellulose from a natural source of cellulose, for example,wood from deciduous and coniferous trees, reeds, bamboo and cottonfibres.

What I claim as my invention is:

l. A method for stabilizing a cellulosic material against degradation byan aqueous alkaline medium that comprises treating the cellulosicmaterial with ferricyanide ion under alkaline conditions.

2. A method as claimed in claim 1 in which the treatment with theferricyanide ion is carried out prior to contacting the cellulosicmaterial with the aqueous alkaline medium.

3. A method as claimed in claim 1 in which the treatment with theferricyanide ion is carried out during contact with the aqueous alkalinemedium.

4. A method as claimed in claim 1 in which the cellulosic material is alignocellulosic material.

5. A method as claimed in claim 4 in which the lignocellulosic materialis wood.

6. A method as claimed in claim 1 in which the cellulosic material iscellulose.

7. A method as claimed in claim 1 in which treatment with theferricyanide ion is carried out at a pH of about 10.

8. A method as claimed in claim 1 in which the ferricyanide ion is addedas potassium ferricyanide.

9. A method as claimed in claim 1 in which the ferricyanide ion is addedas sodium ferricyanide.

10. In a process for the production of pulp useful in paper-making bythe alkaline pulping of a lignocellulosic material the improvementcomprising treating the lignocellulosic material with an alkalinesolution of ferricyanide prior to the pulping.

11. A process as claimed in claim 10 in which the alkaline pulping is bythe soda process.

12. In a process for the production of pulp useful in paper-making bythe alkaline pulping of a lignocellulosic material the improvementcomprising treating the lignocellulosic material with the ferricyanideion during the alkaline pulping.

13. A process as claimed in claim 12 in which the alkaline pulping is bythe soda process.

1. A METHOD FOR STABILIZING A CELLULOSIC MATERIAL AGAINST DEGRADATION BYAN AQUEOUS ALKALINE MEDIUM THAT COMPRISES TREATING THE COLLULOSICMATERIAL WITH FERRICYANIDE ION UNDER ALKALINE CONDITIONS.
 2. A method asclaimed in claim 1 in which the treatment with the ferricyanide ion iscarried out prior to contacting the cellulosic material with the aqueousalkaline medium.
 3. A method as claimed in claim 1 in which thetreatment with the ferricyanide ion is carried out during contact withthe aqueous alkaline medium.
 4. A method as claimed in claim 1 in whichthe cellulosic material is a lignocellulosic material.
 5. A method asclaimed in claim 4 in which the lignocellulosic material is wood.
 6. Amethod as claimed in claim 1 in which the cellulosic material iscellulose.
 7. A method as claimed in claim 1 in which treatment with theferricyanide ion is carried out at a pH of about
 10. 8. A method asclaimed in claim 1 in which the ferricyanide ion is added as potassiumferricyanide.
 9. A method as claimed in claim 1 in which theferricyanide ion is added as sodium ferricyanide.
 10. In a process forthe production of pulp useful in paper-making by the alkaline pulping ofa lignocellulosic material the improvement comprising treating thelignocellulosic material with an alkaline solution of ferricyanide priorto the pulping.
 11. A process as claimed in claim 10 in which thealkaline pulping is by the soda process.
 12. In a process for theproduction of pulp useful in paper-making by the alkaline pulping of alignocellulosic material the improvement comprising treating thelignocellulosic material with the ferricyanide ion during the alkalinepulping.
 13. A process as claimed in claim 12 in which the alkalinepulping is by the soda process.